1. Field of the Invention
The subject invention relates to projection television receivers and, more particularly, to the alignment of the lenses attached to CRT projection tubes in projection television receivers.
2. Description of the Related Art
Projection television receivers provide a way of generating a large television display at an affordable cost. Initially, projection televisions were only available as front projection two-piece combinations including a projector, having the appropriate tuning, audio and video processing circuits and video projecting tubes for projecting light beams containing the picture image, and a separate screen. As with known film projectors, a considerable amount of space is required for these two-piece combinations and care must be taken such that viewers of the display on the screen do not interrupt the light beams being projected to the screen from the projector. These two-piece combination units were followed by one-piece front projection television receivers which folded the light path from the projector to the screen so that both the projector and the screen could be in one housing. However, these one-piece units also required a considerable amount of space. Then followed the advent of rear projection television receivers in which the projector is situated inside the enclosure and projection lenses focus the picture image at an image plane co-planar with the rear projection screen inside of the enclosure. The resultant picture image is then viewable on the other side of the rear projection screen outside of the enclosure.
A rear projection television receiver is shown in FIG. 1. The rear projection television receiver includes a substantially rectangular cabinet 1 having an opening in a front face in which a rear projection screen 2 is ordinarily mounted. The cabinet 1 has mounted therein audio/video processing circuitry (not shown) typically found in television receivers, and a light box 3 containing three projection tubes (cathode ray tubes) for generating light beams modulated with the video signals for the three basic colors red, blue and green, respectively. For convenience, only one projection tube 4 is shown in FIG. 1. A projection lens assembly 5 is associated with the projection tube 4 for focussing the light beam 6 from the projection tube 4, this light beam being directed by mirrors 7 and 8 onto the rear projection screen 2.
In order to provide a satisfactory image on the rear projection screen 2, it is necessary to align the projection tube(s) 4 and the projection lens assembly (assemblies) 5 in the proper direction. Through the experience gained in assembling these rear projection television receivers, the cabinet 1 is manufactured with known mounting surfaces and positioning abutments for the mirrors 7 and 8 such that when mounted, the mirrors 7 and 8 will be in the proper orientation. Similarly, The cabinet 1 is manufactured with a mounting surface and positioning abutments for properly locating the light box 3, which, in turn, is fabricated with mounting surfaces and abutments for properly locating the projection tubes 4 therein. As such, the projection tubes 4 and the associated lenses 5 are xe2x80x9cautomaticallyxe2x80x9d in proper alignment with the mirrors 7 and 8 and the rear projection screen 2. Once assembly of the rear projection television is completed, the alignment of the projection tubes/lenses may be finely adjusted electronically in a known manner. Typically, this is done by activating the audio/video processing circuitry and applying, for example, a test pattern to the projection tube 4. However, as with all manufacturing operations, errors may creep in and, as such, the projection tubes/lenses end up being so far out of alignment that electronic adjustment thereof is impractical. The projection television receiver must then be removed from the assembly line, disassembled and retrofitted.
An object of the invention is to provide a method and apparatus for checking the alignment the lenses of a rear projection television receiver that may be easily performed prior to finishing the assembly of the projection television receiver.
This object is achieved with a lens alignment apparatus for a projection lens assembly of a projection tube in a rear projection television receiver, said apparatus comprising a base having a substantially flat bottom surface, said bottom surface having aligning pins protruding from the bottom surface of the base for frictionally engaging a circumferential surface of the projection lens assembly such that the bottom surface of the base is pressed against a front surface of the lens; a gimbal system having a bottom section mounted to the base, and a top section, said gimbal system having first adjusting means for adjusting the top section with respect to the base in two orthogonal directions in a plane parallel to a plane of the bottom surface of the base, and second adjusting means for angularly adjusting the plane of the top surface with respect to the plane of the bottom surface of the base; and a laser beam generating device mounted on the top section of said gimbal system, whereby said first and second adjusting means enable a laser beam emitted from the laser beam generating device to be coaxial with a central axis of the projection lens assembly.
In use, an operator calibrates the lens alignment apparatus by adjusting the first and second adjusting means such
that the laser beam from the laser beam generating device is coaxial with a reference point on the lens aligning apparatus, this reference point being centered between the aligning pins, and such that the laser beam is orthogonal to the bottom surface of the base of the lens alignment apparatus. The lens alignment apparatus is then positioned on the projection lens assembly and then, by activating the laser beam generating device, a visible red laser beam is generated and reflected by the mirrors, forming a red dot on the rear projection screen 2. The operator may then check the alignment of the projection lens assembly 5 using simple measurements of the position of the red dot on the rear projection screen 2. The lens alignment apparatus is then be removed from the projection lens assembly 5. This is done when the light box is initially installed in the cabinet and can thus obviate unnecessary further assembly if there is an alignment problem.